Volkswagen Golf Service & Repair Manual: Checking systems with an expansion valve, receiver and air conditioner compressor regulating valve -N280- (with externally regulated air conditioner compressor)

Volkswagen Golf Service & Repair Manual / Air conditioning system with refrigerant R134a / Checking pressures on vehicles / Checking systems with an expansion valve, receiver and air conditioner compressor regulating valve -N280- (with externally regulated air conditioner compressor)

Note

Connecting air conditioner service station → Chapter.

Observe the test prerequisites → Chapter.

–	Raise engine speed to 2,000 rpm.

–	Observe air conditioner service station pressure gauge.

Note

Switching pressures for the air conditioner compressor regulating valve -N280- and the radiator fan -V7- are vehicle-specific.

Pressures should be measured at the service connections; the location of these connections is vehicle-specific → Rep. gr.87.

Specifications:

High-pressure side:

Rising from starting pressure (when pressure gauge is connected) to 20 bar.

Low-pressure side:

Falling from starting pressure (when pressure gauge is connected) to diagram value.

A -	Low pressure (measured at the service connection) in bar absolute pressure.

B -	Control current for the air conditioner compressor regulating valve -N280-.

C -	Permitted tolerance range.

Note

Under unfavourable conditions (very high ambient temperatures, high atmospheric humidity), the pressure on the high-pressure side can increase to a maximum of 29 bar.

The control current -B- is indicated in the measured values block.

The high-pressure value measured by the high-pressure sender -G65- is indicated in the measured values block → Rep. gr.87.

The low pressure is adjusted to within tolerances within the output range for the air conditioner compressor depending on the control current for the air conditioner compressor regulating valve -N280-.

Under unfavourable conditions (very high ambient temperatures, high atmospheric humidity), the output may be insufficient to achieve the specification in every case.

The set working current for the regulating valve must be greater than 0.3 A to ensure that the regulating valve is reliably activated.

At the setting “maximum cooling power”, the control current should be approx. 0.65 A to 0.8 A (vehicle-specific, indicated in the measured values block) → Rep. gr.87.

Absolute pressure means that 0 bar corresponds to an absolute vacuum. The normal ambient pressure corresponds to 1 bar absolute pressure. On most pressure gauges, a reading of 0 bar corresponds to an absolute pressure of one bar (which is confirmed by the existence of - 1 bar marking beneath the 0 scale marking).

Checking systems with an expansion valve, receiver and air conditioner compressor regulating valve -N280- (with externally regulated air conditioner compressor)

Possible deviation from specification

Possible cause of fault

Rectifying fault

High pressure remains constant or increases only slightly (above the pressure measured when the engine is stopped).

Low pressure falls quickly to the diagram value or lower.

The required cooling output is not delivered.

Actuation of air conditioner compressor regulating valve -N280- is defective.

Insufficient refrigerant in circuit.

–	Check actuation of air conditioner compressor regulating valve -N280-.

–	Look for leaks using leak detector and rectify them.

–	Recharge refrigerant circuit.

High pressure is normal.

Low pressure matches the diagram value.

The required cooling output is not delivered.

High pressure is normal.

Low pressure too low (see diagram).

The required cooling output is not delivered.

Insufficient refrigerant in circuit.

–	Extract some refrigerant from the refrigerant circuit.

The quantity of refrigerant extracted is significantly less than the prescribed charge quantity.

–	Look for leaks using leak detector and rectify them.

–	Recharge refrigerant circuit.

–	Repeat check.

The quantity of refrigerant extracted is about equal to the prescribed charge quantity.

Expansion valve defective

–	Renew expansion valve.

–	Recharge refrigerant circuit.

–	Repeat check.

Note

If no fault can be found for this complaint, purge (clean) refrigerant circuit with refrigerant R134a → Chapter. If this is not possible in your workshop, blow through refrigerant circuit with compressed air and dry with nitrogen → Chapter.

Check the measured values of the evaporator output temperature sender -G263- or evaporator temperature sensor -G308- and actuation of the air conditioner compressor regulating valve -N280-. If the measured value of the evaporator output temperature sender -G263- or the evaporator temperature sender -G308- is faulty, the evaporator may ice up or the cooling output will not be achieved.

If a repeat test after the expansion valve has been renewed indicates that the air conditioning system is still not operating correctly, refit the expansion valve and purge the refrigerant circuit with compressed air and nitrogen. Then renew the air conditioner compressor and receiver.

In this case, the evaporator may ice up although the correct quantity of refrigerant is present in the refrigerant circuit.

If the expansion valve is defective (always closed or not opening wide enough) the air conditioner compressor regulating valve -N280- will be set to maximum power and the low-pressure value will fall to the diagram value or less (the air conditioner compressor is drawing the refrigerant out of the low-pressure side). However, since no refrigerant can flow through the expansion valve, the required cooling power is not delivered, and it can be that the high-pressure value does not rise at all or not enough, since no energy exchange is occurring.

Possible deviation from specification

Possible cause of fault

Rectifying fault

High pressure increases only slightly above the pressure measured when the engine is stopped.

Low pressure falls only slightly.

The required cooling output is not delivered.

Actuation of air conditioner compressor regulating valve -N280- is defective.

–	Check actuation of air conditioner compressor regulating valve -N280-.

The air conditioner compressor is defective.

–	Extract refrigerant.

–	Purge (clean) refrigerant circuit → Chapter.

–	Renew air conditioner compressor.

–	Recharge refrigerant circuit.

High pressure increases beyond the specification.

Low pressure falls quickly to the diagram value or lower.

The required cooling output is not delivered.

Actuation of air conditioner compressor regulating valve -N280- is defective.

–	Check actuation of air conditioner compressor regulating valve -N280-.

Restriction or obstruction in the refrigerant circuit.

–	Feel the refrigerant circuit with the hand to sense the temperature gradient.

At one component a temperature gradient will be detected:

–	If a hose or pipe is kinked or crushed, renew it.

–	In case of an obstruction, blow through refrigerant circuit with compressed air and nitrogen.

–	Recharge refrigerant circuit.

–	Repeat check.

If no faults are found:

–	Purge (clean) refrigerant circuit → Chapter.

–	Recharge refrigerant circuit.

–	Repeat the check; if the system does not operate correctly

Expansion valve defective.

–	Extract refrigerant.

–	Renew the expansion valve and receiver.

–	Recharge refrigerant circuit.

Note

In this case, the evaporator may ice up although the correct quantity of refrigerant is present in the refrigerant circuit.

Possible deviation from specification

Possible cause of fault

Rectifying fault

High pressure and low pressure are normal at first, but after a time the high pressure increases beyond the specification.

After a time, the low pressure falls to the diagram value or lower.

The cooling power called for is not delivered.

Actuation of air conditioner compressor regulating valve -N280- is defective.

–	Check actuation of air conditioner compressor regulating valve -N280-.

High pressure and low pressure are normal at first, but after a longer drive, the low pressure falls to below the specification (evaporator iced up).

Moisture in the refrigerant circuit.

–	Extract refrigerant.

–	Blow through refrigerant circuit with compressed air and nitrogen.

–	Renew receiver together with dryer.

–	Evacuate refrigerant circuit for at least 3 hours.

–	Recharge refrigerant circuit.

–	Repeat the check; if the function is not OK

–	Purge (clean) refrigerant circuit → Chapter.

–	Recharge refrigerant circuit.

–	Repeat check.

Note

If this complaint occurs after a longer period of operation or only occasionally (the low pressure falls below the specification and the evaporator ices up) it is sufficient only to renew the dryer (fitted within the receiver). Check the quantity of refrigerant oil. Then evacuate the refrigerant circuit for at least 3 hours.

In case of this complaint, it is not initially necessary to purge the refrigerant circuit with compressed air and nitrogen, since as a rule only a small quantity of moisture will have accumulated in the system, which can be removed by a longer evacuation period.

In this case, the evaporator may ice up although the correct quantity of refrigerant is present in the refrigerant circuit.

Possible deviation from specification

Possible cause of fault

Rectifying fault

High pressure normal, low pressure too low (see diagram), the required cooling power is delivered.

Actuation of air conditioner compressor regulating valve -N280- is defective.

–	Check actuation of air conditioner compressor regulating valve -N280-.

Expansion valve defective.

–	Extract refrigerant.

–	Purge (clean) refrigerant circuit → Chapter.

–	Renew the expansion valve and receiver.

–	Recharge refrigerant circuit.

–	Repeat the check; if the system does not operate correctly

–	Renew the air conditioner compressor.

The air conditioner compressor is defective.

–	Extract refrigerant.

–	Purge (clean) refrigerant circuit → Chapter.

–	Renew the air conditioner compressor.

–	Recharge refrigerant circuit.

–	Repeat check.

Note

If the fault is “high pressure normal, low pressure too low ” note the following: if faulty the evaporator could ice up or the required cooling output is not delivered.

In this case, the evaporator may ice up although the correct quantity of refrigerant is present in the refrigerant circuit.

Check the measured values of the evaporator output temperature sender -G263- or evaporator temperature sensor -G308- and actuation of the air conditioner compressor regulating valve -N280-. If the measured value at the high-pressure sender -G65- is faulty, the evaporator can ice up or the required cooling power is not delivered.

If the defect is in the air conditioner compressor regulating valve -N280- (the regulating valve is not activated, but the air conditioner compressor still runs), it is not necessary to blow through the refrigerant circuit. If this fault occurs, it is sufficient to renew the air conditioner compressor (check the refrigerant oil quantity in the air conditioner compressor).

→ Rep. gr.87

Possible deviation from specification

Possible cause of fault

Rectifying fault

High pressure normal or too high.

Low pressure too low (see diagram).

The air conditioner compressor is noisy (especially immediately after being switched on).

The required cooling output is not delivered.

Actuation of air conditioner compressor regulating valve -N280- is defective.

Too much refrigerant in circuit.

–	Check actuation of air conditioner compressor regulating valve -N280-.

–	Extract some refrigerant from the refrigerant circuit.

The quantity of refrigerant extracted is about equal to the prescribed charge quantity:

–	Renew the air conditioner compressor.

The quantity of refrigerant extracted is significantly greater than the prescribed charge quantity:

–	Recharge refrigerant circuit.

–	Repeat check.

Too much refrigerant oil in circuit.

–	Drain refrigerant circuit.

The quantity of refrigerant extracted is about equal to the prescribed charge quantity.

–	Purge (clean) refrigerant circuit → Chapter.

–	Recharge refrigerant circuit.

–	Repeat check.

Expansion valve defective.

–	Drain refrigerant circuit.

–	Renew the expansion valve and receiver.

–	Recharge refrigerant circuit.

–	Repeat the check; if the system does not operate correctly

–	Renew the air conditioner compressor.

The air conditioner compressor is defective.

–	Drain refrigerant circuit.

–	Purge (clean) refrigerant circuit → Chapter.

–	Renew the air conditioner compressor.

The quantity of refrigerant extracted is significantly greater than the prescribed charge quantity.

–	Recharge refrigerant circuit.

–	Repeat check.

Note

Overfilling with refrigerant oil can occur if the refrigerant oil level was not checked after the air conditioner compressor was renewed.

If the air conditioner compressor is not to be replaced, drain refrigerant oil from air conditioner compressor via the drain plug. From the total amount of refrigerant oil, fill 50 g direct into air conditioner compressor and fill remainder in refrigerant circuit according to → vehicle-specific workshop manual.

Possible deviation from specification

Possible cause of fault

Rectifying fault

High pressure and low pressure are normal.

The required cooling output is not delivered.

Actuation of air conditioner compressor regulating valve -N280- is defective.

Too much refrigerant oil in circuit.

–	Check actuation of air conditioner compressor regulating valve -N280-.

–	Purge (clean) refrigerant circuit → Chapter.

High pressure and low pressure are normal.

The air conditioner compressor is noisy (especially immediately after being switched on).

The cooling power required is delivered.

Too much refrigerant oil in circuit.

–	Drain refrigerant circuit.

–	Purge (clean) refrigerant circuit → Chapter.

–	Recharge refrigerant circuit.

–	Repeat check.

Expansion valve defective.

–	Renew expansion valve.

Note

Overfilling with refrigerant oil can occur if the refrigerant oil level was not checked after the air conditioner compressor was renewed.

If the expansion valve is defective (always open) the evaporator temperature will no longer be regulated so that only gaseous refrigerant exits the evaporator. It is then possible that under certain operating conditions, drops of liquid will be drawn into the air conditioner compressor, which will hen cause noise (because liquid is incompressible).

With expansion valve, receiver and electrical air conditioner compressor

Note

The electrical air conditioner compressor does not have an air conditioner compressor regulating valve -N280-. Regulation takes place via the speed of the air conditioner compressor. The air conditioner compressor contains the control electronics and a G-supercharger that impels the refrigerant.

Checking systems with a restrictor and reservoir and air conditioner compressor regulating valve -N280- (with externally regulated air conditioner compressor)

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